1. Field of the Invention
The present invention relates to a method and apparatus for qualitatively analyzing high-molecular additives in a metal plating solution, and, more particularly, to a method and apparatus for qualitatively analyzing high-molecular additives in a metal plating solution, by which the state of a sample to be qualitatively analyzed is optimized by removing excess sulfate ions and metal ions from a metal plating solution without degrading high-molecular additives, and then the specific structure and molecular weight of a very small amount of high-molecular additives can be measured.
2. Description of the Related Art
A metal plating solution may include sulfuric acid (H2SO4), copper sulfate (CuSO4) and hydrochloric acid (HCl), each of which is a basic chemical commonly used in the metal plating solution, and three kinds of additives, each of which is a chemical controlling the characteristics of plating. The three kinds of additives are as follows.
First, there is a brightener, serving to physically increase plating density by adsorbing the brightener on a plating surface and thus making plating particles dense. Typically, the brightener, which is a water-soluble sulfonic acid containing a mercapto group and a thio group, exists in a plating solution in an anionic state.
Second, there is a leveler (strong plating suppressor) serving to smooth and flatten the entire plating surface by bonding to the high current density portion of a reduction electrode surface. The leveler exists in an acidic plating solution as an organic compound containing a cationized nitrogen atom.
Third, there is a carrier (mild plating suppressor) serving to provide improved plating thickness distribution by preventing metal ions from being concentrated on only the high current density portion of a reduction electrode surface (by preventing the polarization of the concentration of metal ions), thus applying uniform plating current, thereby controlling the overall plating rate. The carrier is necessarily required in order to form plating particles having a minutely oriented structure by forming a stable diffusion layer on the surface of a reduction electrode at the time of electroplating, thus controlling the concentration of brightener, carrier and chloride ions. Typically, as the carrier, a high molecular weight material, such as polyethylene glycol (PEG), polypropylene glycol (PPG), or the like, is used.
Since these high-molecular additives, which are used for plating, play a very important role in the characteristics of plating, it is necessary to control them. However, currently, component analysis (qualitative analysis) thereof is not conducted, and only the concentration thereof is controlled. Further, methods of measuring absolute concentrations of a very small amount of organic high-molecular additives present in strong acid are not known.
A method of analyzing the concentrations of organic high-molecular additives in an electrolytic copper sulfate plating solution, which is generally conducted in this field, is a cyclic voltammetric stripping (CVS) method, which is an electrochemical measurement method. In this method, the concentrations of the additives are not individually analyzed, and the concentrations thereof are merely indirectly controlled by changing the voltages of all the additives, thus decreasing accuracy and repeatability. That is, it is not absolutely useful to control the concentrations of the additives through the change in voltages of all the additives.
In particular, among the above high-molecular additives, the carrier has electroplating activity when it can play the above role at the time of electroplating. In this case, when the molecular weight of the carrier is increased, the electroplating activity of the carrier is increased, and when the molecular weight thereof is decreased, the electroplating activity thereof is decreased. In particular, a high-molecular additive used as the carrier must have a molecular weight of 4000 Da or more in order to have electroplating activity. When the molecular weight of the high-molecular additive is decreased to 1000 Da or less, the high-molecular additive lose electroplating activity, so that it cannot serves as a carrier, with the result that plating becomes poor. That is, in order to improve throwing power at the time of plating, the plating rate must be controlled by increasing the electroplating activity of the high-molecular additive for a carrier, and, in order to control the plating rate, a high-molecular additive for a carrier having a molecular weight of 4000 Da or more must be selected, and the selected high-molecular additive must be maintained to have a molecular weight of 4000 Da or more even when plating.
As described above, the physical properties of high-molecular materials are determined by the molecular weight, repetitive units and end group structure thereof, rather than by the concentration thereof. That is, the electroplating activity of the high-molecular material can be evaluated by measuring the molecular weight thereof, and the reactivity of the high-molecular material can be evaluated by analyzing the chemical structure thereof. In conclusion, in the case of the high-molecular additives used in plating, the analysis of the molecular weight and chemical structure thereof is necessarily required.
In particular, in the case of a high-molecular additive for a carrier, since the high-molecular additive is degraded in fragments on the surface of an electrode and thus a stable diffusion layer cannot be formed, the analysis of the molecular weight thereof must be conducted in order to evaluate the electroplating activity thereof at the time of plating. Further, since the repetitive unit and end group of a high-molecular material influence the reactivity thereof, the repetitive unit and end group thereof must also be accurately analyzed.
However, the analysis of the molecular weight and structure of high-molecular additives present in a metal plating solution in very small quantities is not conducted at present.